I can't speak to the vibrancy of the French Struts2 community in general, or the viability of whatever forum you're talking about. I think looking at the
Struts mailing lists at Apache would be a more reliable indicator, though.
Also note that Struts 2 has not become nearly as popular as Struts 1 (and won't ever, IMO).
To deduce from either of these facts that is it obsolete would depend on your exact definition of "obsolete". I wouldn't use it for new projects, though, as I think that better alternatives are available.